Ultrasound uses sound waves of frequency in the range of megahertz (millions of cycles or waves per second). Typically this ranges from 3.5 MHz-10 MHz. Most modern day probes are multi frequency i.e.: one can switch from lower to higher frequencies. Why so? Simple – lower the frequency (3-3.5Mhz) deeper the penetration of the sound beam; but the resolution (or quality of image) is poorer. The higher the frequency, it is just the opposite.

Thus, large structures like the liver, kidneys and spleen are imaged using frequencies ranging from 3 to 3.5 MHz. For superficial structures like the orbits (eyes), the testes and breast, the frequencies typically used, are in the range of 5-10MHz. The reflected sound waves are converted back to electrical signals in the probe and transmitted to the processing device (a high speed computer) which displays the image on the monitor.

Note: We now have a new site at: http://www.ultrasound-images.com/ where you can find many more high resolution ultrasound images on all topics ranging from the hepatobiliary system to obstetric and fetal sonography.

II) Hypoechoic/ hyperechoic etc:

Bright (or white areas) represent high relfectivity or reflective surfaces / interphases in the body. Hypoechoic- blacker or low signal reflection areas are called hypoechoic. Anechoic structures are usually filled structures like blood, urine etc. Bone, air and calcium contaning lesions (like stone) appear intensely bright (whiter) or hyperechoic. An acoustic shadow (dark area) is seen behind such structures. Structures like the liver and pancreas appear in various shades of gray depending upon their echogenicity (ability to reflect ultrasound waves). See th images below: the first is an ultrasound image of the gall bladder. This shows typical anechoic nature of the bile in the bladder (appears dark).

The image below shows the anechoic urine in the urinary bladder (dark) with a calculus (hyperechoic) appearing white; note the well defined shadow beyond the calculus.

The following images of the uterus show a large mass in the uterus, a fibroid (approximately 12 x 7 cms.). This shows a typical soft tissue echogenicity. This means its echogenicity is between that of a calculus and the urinary bladder (fluid). The soft tissue mass, typically, appears grey.

Further, an important point to note is that with a change in the scan plane, i.e. the plane of the probe, one can get sagittal or transverse sections of the part ( the uterus). In fact, it is easy to obtain any plane of section of the organ being viewed, by changing the position, plane, angle etc., of the ultrasound probe.